Lubricating oil additives

ABSTRACT

THE INVENTION PROVIDES A LUBRICATING OIL ADDITIVE CONSISTING ESSENTIALLY OF A MIXTURE OF AT LEAST ONE BISMUTH DIHYDROCARBYL DITHIOPHOSPHATE AND AT LEAST ONE SALT OF A DIHYDROCARBYL DITHIOPHOSPHORIC ACID AND A METAL OF GROUP IIB OF THE PERIODIC TABLE SELECTED FROM THE GROUP CONSISTING OF ZINC DIHYDROCARBYL DITHIOPHOSPHATES AND CADMIUM DIHYDROCARBYL DITHIOPHOSPHATES, WHICH ADDITIVE MAY BE ADMIXED WITH AN OIL OF LUBRICATING VISCOSITY, FOR EXAMPLE IN AN AMOUNT OF FROM 0.01% TO 10% BY WEIGHT BASED ON THE TOTAL WEIGHT OF THE OIL AND ADDITIVE.

United States Patent Ofice 3,595,792 Patented July 27, 1971 3,595,792 LUBRICATING OIL ADDITIVES John Scotchford Elliott and Gerald John Joseph Jayne, London, and Anthony David Brazier, Wokingham, Berkshire, England, assignors to Castrol Limited, London, England No Drawing. Filed Apr. 4, 1968, Ser. N0. 718,930 Claims priority, application Great Britain, Apr. 5, 1967, 15,726/67 Int. Cl. ClOm 1/48 US. Cl. 25232.7 9 Claims ABSTRACT OF THE DISCLOSURE The invention provides a lubricating oil additive consisting essentially of a mixture of at least one bismuth dihydrocarbyl dithiophosphate and at least one salt of a dihydrocarbyl dithiophosphoric acid and a metal of Group III) of the Periodic Table selected from the group consisting of zinc dihydrocarbyl dithiophosphates and cadmium dihydrocarbyl dithiophosphates, which additive may be admixed with an oil of lubricating viscosity, for example in an amount of from 0.01% to 10% by weight based on the total weight of the oil and additive.

This invention relates to lubricating oil additives and lubricating compositions containing them.

It is Well known that the metal salts of the diesters of phosphorothiolthionic acids, generally known as dithiophosphoric acids, are useful as additives for lubricants. The diesters may be prepared by the reaction of alcohols or phenols with phosphorus pentasulphide and then converted into metal salts by direct reaction with a metal oxide or hydroxide.

Though salts of a wide variety of metals have been suggested as additives for lubricants and are effective to a greater or less degree, the zinc salts are almost universally preferred on account of their greater oil-solubility and ease of preparation.

It has been well known for some time that organic zinc dithiophosphates when used as additives for lubricants, are effective inhibitors of oxidation and corrosion of composite metal, e.g. copper-lead, bearings and enhance the load-carrying capacity of the oil. These compounds have the valuable property of reducing wear of valve tappets which sometimes takes place under heavy load.

According to the present invention there is provided a lubricating oil additive comprising a mixture of one or more bismuth dihydrocarbyl dithiophosphates and one or more zinc or cadmium dihydrocarbyl dithiophosphates.

The invention also provides a lubricating oil additive comprising a mixture of a bismuth dihydrocarbyl dithiophosphate and a zinc dihydrocarbyl dithiophosphate. The hydrocarbyl group may be alkyl, alkaryl, aralkyl or aryl which group may be substituted by hydroxyl, halogen or ether groups. The hydrocarbyl groups of any acid component of the mixture may be the same or different, and mixtures of acids may be used in the preparation of the additives according to the invention.

The invention further provides a lubricating composition comprising a major proportion of an oil of lubricating viscosity having admixed therewith a minor proportion of an additive comprising one or more bismuth dihydrocarbyl dithiophosphates and one or more zinc or cadmium dihydrocarbyl dithiophosphates.

The amount of the bismuth in relation to the total weight of bismuth and zinc and/0r cadmium present in the dihydrocarbyl dithiophosphates will generally be from 5%, preferably 10% to and more preferably from 10 to 60%. In one aspect of the invention the bismuth is present in an amount of 10% to 30% by weight on the total weight of bismuth and zinc and/or cadmium present in the dihydrocarbyl dithiophosphates.

In a preferred form of the invention the additive is a substantially neutral mixed salt of one or more dihydrocarbyl dithiophosphoric acids containing both bismuth and either zinc or cadmium, which may be prepared, for example, by partially neutralising the dithiophosphoric acid or mixture of acids with bismuth oxide or with a mixture of bismuth and zinc or cadmium oxides, the final neutralisation step being achieved by further reacting with zinc or cadmium oxide. In this manner substantially neutral products can be obtained whereas it is not in general possible to obtain bismuth dithiophosphates free front acidic impurities when using bismuth oxide.

Accordingly the invention includes a method of pre paring a lubricating oil additive which method comprises partially neutralising a dihydrocarbyl dithiophosphoric acid or a mixture of dihydrocarbyl dithiophosphoric acids with bismuth oxide or hydroxide or a mixture of bismuth oxide or hydroxide and zinc oxide or hydroxide or cadmium oxide or hydroxide and further reacting the product with zinc oxide or hydroxide or cadmium oxide or hydroxide to provide a substantially neutral, as hereinafter defined, mixture of one or more bismuth dihydrocarbyl dithiophosphates and one or more zinc or cadmium dihydrocarbyl dithiophosphates.

By substantially neutral" is meant that either the acidity of the salt, when determined in a solution consisting of 60 volume percent benzene and 40 volume percent neutralised industrial methylated spirit containing 1 ml. of lacmoid indicator per mls. of solvent, is not more than about 1 mg. KOH/g., the solution preferably being neutral or alkaline to the indicator; or that the pH of the salts is greater than 4 and preferably greater than 5, when determined on the pH meter by dissolving 1.5 g. of sample in a mixture of 60 ml. aqueous alcohol (67% alcohol 33% water by volume) and 40 ml. ether.

The additives of the present invention have improved load carrying properties as compared with the corresponding conventional zinc dialkyl dithiophosphates. They also impart improved oxidation resistance to the oil. In comparison with the corresponding simple bismuth dithiophosphates the substantially neutral mixed salts prepared as hereinbefore described have improved thermal stability in lubricating compositions and show less tendency to promote wear under low loads.

The dihydrocarbyl dithiophosphoric acid or mixtures thereof may be made by reacting one or more alcohols or phenols or a mixture thereof with phosphorus pentasulphide.

In a further aspect of the invention the mixture of salts may be prepared by making separately one or more bismuth dihydrocarbyl dithiophosphates and one or more dihydrocarbyl dithiophosphates of zinc or cadmium and thereafter mixing the salts together. The alcohols which may be used alone or in admixture in preparing the dihydrocarbyl dithiophosphoric acids may be selected from the following:

4 hour. The product was then vacuum stripped at 80 C. at about 10 mm. pressure to remove excess alcohols.

The additive so obtained was alkaline to lacmoid indicator and had a pH of 6.5. It had the following analysis:

131.68% (calc. 6.56%) Zn, 6.01% (calc. 6.35%) P, 8.94% (calc. 8.96%)

The weight ratio of the bismuth and zinc in this mixed salt was therefore approximately 1:1.

Further examples of the preparation of compounds according to the present invention are given in Table l, the same dithiophosphoric acid being used as in Example 1 and the method of preparation being substantially the same in each case. The only difference was in the ratio of bismuth oxide to zinc oxide employed. All these products were alkaline to lacmoid indicator and had pl-Is in the range 6.16.6.

TABLE I.BIS.\1UTII 'ZINC DITIIIOPHOSPIIATES FROM DTPAJ ZnO B1903 Percent Bl Percent Zn Weight ratio, Example No. Wt. tg.) Moles Wt. (g) Moles Found Calcd Found Calc'd BizZn The phenols may be alkylated phenols, particularly P- EXAMPLE 5 octyl phenol, p-nonyl phenol and heptyl phenol. The mixture of salts according to this invention may be formed from any of the acids or mixtures of acids described in British patent specification No. 822,655. In one aspect of the invention each hydrocarbyl group in the dihydrocarbyl dithiophosphate contains from 3 to 8 carbon atoms.

The invention also includes mixtures of the additives described above with lubricating oils, either in the form of concentrates or otherwise.

The invention further includes a lubricating oil composition wherein the amount of additive in the composition is from 0.01 to 10%, preferably from 0.1 to 2.0%, by weight on the weight of the composition.

The lubricating oil composition according to the invention may also include conventional additives, such as viscosity index improvers, corrosion inhibitors, detergents, dispersants etc. The compositions will preferably contain alkaline earth metal sulphonate detergents or barium salts of phosphorsulphurised hydrocarbons such as polyisobutylene, ashless dispersants such as polyisobutenyl succinimides and viscosity index improvers such as long chain alkyl polymethacrylates or polyisobutylene.

The preparation of additives according to the present invention will now be illustrated with reference to the following examples.

EXAMPLE 1 Preparation of bismuth/zinc (1:1) salt of DTPA-1 The dithiophosphoric acid (133 g. 0.5 mole) was run in a slowly from the tap funnel at such a rate as to maintain the temperature at about C. (about 30 minutes). The remainder of the zinc oxide was then added, the total amount of zinc oxide added being 14.52 g. (0.178 mole) and the mixture was then stirred at 60 C. for a further Preparation of bismuth/zinc (1:1) salt of DTPA-2 A mixture of dialkyl dithiophosphoric acids was prepared from isopropanol (199 g., 3.32 moles), capryl alcohol (600 g., 4.62 moles) and phosphorous pentasulphide (378 g. 17 moles) in the manner described in Example 1, but at a temperature of C.

Employing essentially the same method as described in Example 1 this dithiophosphoric acid (DTPA-Z) (169 g. 0.5 moles) was added to a mineral oil slurry of bismuth and zinc oxides, the reaction being completed by the addition of further zinc oxide as described in Example 1. The weights of bismuth and zinc oxide employed were 13.97 g. (0.03 mole) and 14.52 g. (0.178 mole) respectively. The product had an acidity of 0.7 mg. KOH/g. and a pH of 5.3. It analysed as follows:

Bi, 6.4% (calc. 6.2%) Zn. 4.9% (calc. 6.4%) P, 7.44% (calc. 7.8%)

EXAMPLE 6 Preparation of bismuth/zinc (1 :1) salt of di-(2- ethyl hexyl) dithiophosphoric acid Employing essentially the same method as described in Example 1, di-Z-ethylhexyl dithiophosphoric acid (111 g. 0.2 mole), prepared from Z-ethyl hexanol (1040 g. 8.0 moles) and phosphorus pentasulphide (444 g. 2.0 moles) at 8090 C. was added to a mineral oil slurry of bismuth oxide and zinc oxide, the weights of bismuth and Zinc oxides employed being 8.4 g. (0.018 mole) and 8.75 g. (0.107 mole) respectively.

The product had an acidity of 0.93 mg. KOH/g. and a pH of 4.7. It analysed as follows:

Bi, 4.3% (calc. 5.15%) Zn, 4.8% (calc. 4.95%) P, 6.75% (calc. 6.45%)

EXAMPLE 7 Preparation of bismuth/cadmium (1:1) salt of di(2- ethyl hexyl) dithiophosphoric acid I Employing essentially the same method as described m Example 1, di-Z-ethylhexyl dithiophosphoric acid (114.3 g.0.3 mole), from a subsequent preparation similar to that in Example 6, was added to a mineral oil slurry of bismuth oxide and cadmium oxide, the weights of the bismuth and cadmium oxides being 11.6 g. (0.025 mole) and 11.3 g. (0.09 mole) respectively.

The product had an acidity of 0.56 mg. KOG/g. and a pH of 4.4. It analysed as follows:

Bi, 5.6% (calc. 6.6%) Cd, 7.3% (calc. 6.6%) P, 6.46% (calc. 6.1%)

EXAMPLE 8 Preparation of bismuth salt of DTPA1 This was prepared as described in Example 1 except that all the bismuth oxide (42.7 g. 0.0917 mole) was added at the beginning to the DTPA-l (133 g. 0.5 mole). Twice the normal amount of mineral oil (48 g.) was required to maintain a clear solution. The additive had the following analysis:

Bi, 15.0% (calc. 14.7%) P, 6.59% (calc. 6.64%)

The additive was obtained by mixing 20% by weight of the above prepared bismuth salt with 80% by weight of a similarly prepared zinc salt of the same acid.

In order to demonstrate the antioxidant properties of the additives of the present invention in a typical lubricating oil, blends were prepared in mineral oil A, which was a solvent refined mineral oil of viscosity approximately 160 seconds Redwood 1 at 140 F. These blends were all made up to contain 0.072% phosphorus and comparison was made with certain conventional zinc dialkyl dithiophosphates and with bismuth dialkyl dithiophosphates which did not contain zinc or cadmium. These oils were subjected to the well-known Rotary Bomb test, a description of which is given in British patent specification No. 1,023,380 on page 12 lines -22. The results of these tests and the conditions employed are given on Table II. The advantage of the additives of the present invention over the corresponding zinc or cadmium dithiophosphates is clearly seen from this table and in some cases the additives of the present invention also show an advantage over the simple bismuth salts.

When the load carrying properties of the additives of the present invention are compared with those of the corresponding zinc dithiophosphates on the 4-ball machine at room temperature by the standard procedure employ ing a series of l-minute runs at different loads, a distinct improvement in load carrying capacity is consistently obtained as judged by a comparison of the wear scar diameters at loads above the point of incipient seizure. In general it has been found that the higher the amount of bismuth dithiophosphate in the oil the smaller the wear scar diameter. When, however, wear tests are carried out on the 4-ball machine at low loads the amount of wear given by the bismuth dithiophosphates is significantly greater than that given by the corresponding zinc dithiophosphates. The additives of the present invention, particularly the substantially neutral products obtained by the preferred method of preparation, often show a smaller increase in wear than would be anticipated from the amount of bismuth present. This is illustrated in Table III, which compares the results of tests carried out on blends of several dithiophosphates in mineral oil A, all these blends containing 0.056% phosphorus. The 4-ball machine was operated for periods of l-hour under a 15 kg. load, the oil temperature being 50 C. It can be seen from Table III that additives of the present invention gave, under these conditions, wear scar diameters not greatly in excess of the corresponding zinc dithiophosphates, whereas the simple bismuth salts gave substantially increased wear.

TABLE II.-ROTARY BOMB TEST Temperature 150 C. 3 metres of copper wire Initial pressure .10 p.s.i.

Induction period Additive Percent (minutes) None 20 Zinc salt of D'IPA-i.. 0.75 233 Bismuth salt at DIPA-l 1.08 275 Product of Example:

Zinc salt of UTPA 0. 98 100 Bismuth salt of DTPA 0. 975 240 Product of Example 5- 0. U? 237 Cadmium di (Z-ethyl huxyl) dithiophosphate. 1.22 280 Bismuth di (Bethyl liexyl) ditliiophosphato 1. i7 271 Product of Example 7 1.11 300 TABLE III.4BALL WEAR TESTS (i5 kg.1 hr. -50 C.)

Precent inc.

Mean wear in wear over scar diam. zinc com- Additive Percent tmm.) pound Zinc salt of DTPA-i 0. 58 0. 206

Bismuth salt of DIPA-l 0. S4 0. 433 46 Product of Example:

0. 286 Nil phosphate 0. 915 0. 400 35 Product of Example 6 0. 83 0. 312 6 We claim:

1. A lubricating oil additive consisting essentially of a mixture of at least one bismuth dihydrocarbyl dithiophosphate and at least one salt selected from the group consisting of zinc dihydrocarbyl dithiophosphates and cadmium dihydrocarbyl dithiophosphates, wherein each hydrocarbyl group contains from 3 to 15 carbon atoms and wherein the amount of bismuth present is from 5% to by weight of the total bismuth and zinc or cadmium present in the dihydrocarbyl dithiophosphates.

2. A lubricating oil additive as claimed in claim 1 wherein each hydrocarbyl group is an alkyl group containing from 3 to 8 carbon atoms.

3. A lubricating oil additive as claimed in claim 1 wherein the amount of bismuth present is from 10% to 60%.

4. A lubricating oil additive as claimed in claim 1 when prepared by partially neutralising a member of the group consisting of dihydrocarbyl dithiophosphoric acids and mixtures thereof with a member of the group consisting of bismuth oxide, bismuth hydroxide, a mixture of bismuth oxide and zinc oxide, a mixture of bismuth oxide and zinc hydroxide, a mixture of bismuth hydroxide and zinc oxide, a mixture of bismuth hydroxide and zinc hydroxide, a mixture of bismuth oxide and cadmium hydroxide, a mixture of bismuth oxide and cadmium oxide, a mixture of bismuth hydroxide and cadmuim oxide, and a mixture of bismuth hydroxide and cadmium hydroxide and further reacting the partially neutralised product with a member of the group consisting of zinc oxide, zinc hydroxide, cadmium oxide and cadmium hydroxide to provide a substantially neutral mixture of at least one bismuth dihydrocarbyl dithiophosphate and at least one member of the group consisting of zinc dihydrocarbyl dithiophosphates and cadmium dihydrocarbyl dithiophosphates.

5. A lubricating oil additive as claimed in claim 1 consisting essentially of a bismuth dihydrocarbyl dithio phosphate and a zinc dihydrocarbyl dithiophosphate.

6. A lubricating oil additive as claimed in claim 5 wherein the amount of bismuth present is from 10% to 90% by weight of the total weight of bismuth and zinc present in the dihydrocarbyl dithiophosphate.

7. A lubricating oil additive as claimed in claim 5 in admixture with an oil of lubricating viscosity, the additive being admixed with the oil in an amount of from 0.01% to 10% by weight based on the total weight of the oil and additive.

8. A lubricating oil additive as claimed in claim 1 in admixture with an oil of lubricating viscosity, the additive being admixed with the oil in an amount of 0.01% to 10% by Weight based on the total weight of the oil and additive.

9. A lubricating oil additive as claimed in claim 7 admixed with the oil in an amount of from 01% to 2% by weight.

References Cited DANIEL E. WYMAN, Primary Examiner 10 I. VAUGHN, Assistant Examiner US. Cl. X.R. 252400 

